Radiofrequency catheter ablation is a catheterization laboratory technique for the cure of cardiac arrhythmias, which has become common in pediatric cardiology practice. Recent analyses have suggested that ablation therapy is more cost-effective compared not only with surgery, but also with antiarrhythmic medication. Despite a good initial success rate of the technique, and a low initial complication rate, there is concern about possible long-term effects with the technique in the pediatric age group. There are reports not only of damage to cardiac valves, but also the development of new arrhythmias, including sudden death, as a result of ablations in children. Recurrences are observed frequently following initially successful procedures. Finally, there are animal data to suggest that immature myocardium is more prone to severe damage as a result of ablation procedures. Few, if any, data exist to support the long-term safety of these ablation techniques in children. Therefore, before ablation therapy becomes the standard approach in children, it is important to carefully assess the long-term risks in this patient group. The application presents plans to conduct a multi-center, prospective, 5-year study to evaluate children undergoing catheter ablation at pediatric centers in North America. The collection of these data is intended to provide the following information: 1) the incidence of serious cardiac damage as a result of ablation; 2) the incidence and time course of recurrence after initially successful ablation; and 3) the incidence of proarrhythmia following ablation. A total of 450 pediatric patients will be enrolled prospectively and evaluated both before ablation of supraventricular tachycardia and at intervals following ablation with clinical history and examination, electrocardiogram, 24-hour Holter monitor, and echocardiogram, with non-invasive studies read by outside consultants. In addition, a complete Registry of pediatric patients undergoing ablation at the participating centers will be established to allow comparisons with the study group and to provide population estimates of success and complication rates.